Low friction polish-stop stratum for endpointing chemical-mechanical planarization processing of semiconductor wafers

Abstract

The present invention is a semiconductor wafer that enhances polish-stop endpointing in chemical-mechanical planarization processes. The semiconductor wafer has a substrate with a device feature formed on the substrate, a stratum of low friction material positioned over the substrate, and an upper layer deposited on the low friction material stratum. The low friction stratum has a polish-stop surface positioned at a level substantially proximate to a desired endpoint of the chemical-mechanical planarization process. The upper layer, which is made from either a conductive material or an insulative material, has a higher polishing rate than that of the low friction stratum. In operation, the low friction stratum resists chemical-mechanical planarization with either hard or soft polishing pads to stop the planarization process at the desired endpoint.

We claim: 
     
       1. A method of chemical-mechanical planiarization of a semiconductor wafer, comprising: sputtering a graphitic carbon stratum to a thickness of approximately 100 Å to approximately 600 Å over a semiconductor substrate to form a polish-stop surface of low friction material positioned at a level substantially proximate to a desired end-point:   covering the low friction stratum with an upper layer of material having a polishing rate higher than that of the graphitic carbon stratum:   mounting the substrate to a wafer carrier of a chemical-mechanical planarization machine   pressing the upper layer against a polishing pad of the chemical-mechanical planarization machine in the presence of a slurry; and   moving at least one of the wafer carrier or the polishing pad to impart relative motion between the wafer and the polishing pad, wherein the graphitic carbon stratum resists the planarization pad to substantially stop the planarization process at the desired end-point.   
     
     
       2. The method of claim 1 wherein the graphitic carbon stratum is sputtered to a thickness of approximately 100 Å to approximately 300Å. 
     
     
       3. The method of claim 1 wherein the graphitic carbon is deposited on the insulative layer at a temperature of approximately 50° C. to approximately 350° C. 
     
     
       4. The method of claim 1 wherein the graphitic carbon is deposited on the insulative layer at a temperature less than 75° C. 
     
     
       5. The method of claim 1 wherein the polishing pad has a Rockwell hardness of at least approximately 75. 
     
     
       6. The method of claim 1 wherein the polishing pad has a Rockwell hardness of at least 90. 
     
     
       7. The method of claim 1 wherein the slurry is an aggressive slurry having abrasive particles made from aluminum dioxide. 
     
     
       8. The method of claim 6 wherein the slurry is an aggressive slurry having abrasive particles made from aluminum dioxide. 
     
     
       9. A method of chemical-mechanical planarization of a semiconductor wafer, comprising: depositing a graphitic carbon stratum to a thickness between approximately 100 Å and 600 Å over a semiconductor substrate to form a polish-stop surface of low friction material positioned at a level substantially proximate to a desired end-point;   covering the low friction stratum with an upper layer of material having a polishing rate higher than that of the graphitic carbon stratum;   mounting the substrate to a wafer carrier of a chemical-mechanical planarization machine;   pressing the upper layer against a polishing pad having a Rockwell hardness of at least 75 with a downforce of at least 7 psi; and   moving at least one of the wafer carrier or the polishing pad to impart relative motion between the wafer and the polishing pad in the presence of a slurry, wherein the graphitic carbon stratum resists the planarization pad to substantially stop the planarization process at the desired end-point.   
     
     
       10. The method of claim 9 wherein the graphitic carbon stratum is sputtered to a thickness of approximately 100 Å to approximately 300 Å. 
     
     
       11. The method of claim 9 wherein the graphitic carbon is deposited on the insulative layer at a temperature of approximately 50° C. to approximately 350° C. 
     
     
       12. The method of claim 9 wherein the graphitic carbon is deposited on the insulative layer at a temperature less than 75° C. 
     
     
       13. The method of claim 9 wherein the polishing pad has a Rockwell hardness of at least 90. 
     
     
       14. The method of claim 13 wherein the slurry is an aggressive slurry having abrasive particles made from aluminum dioxide. 
     
     
       15. The method of claim 9 wherein the slurry is an aggressive slurry having abrasive particles made from aluminum dioxide.